8/24/2016 Pour Plate Method Analysis colonies embedded in the agar Colony Forming Units CFU In theory,one CFU arises from one cell may not be true -may arise from clusters/chains of cells -may give an underestimation of the number of bacteria in a sample Cells need to be separated Sample homogenization Sample dilution Countable plate Analysis contains 25 250 colonies Roll Tube Method ·Fewer or more ·Same as pour plate colonies affect but tubes are used accuracy Total number: d Bacterial dilution is multiply the added to 2 ml molten colomy count by agar in a tube and the dilution rolled around in cold factor water until solid ·Advantage-less 品 plate count agar is used 58/24/2016 5 Pour Plate Method colonies embedded in the agar 17 Analysis Colony Forming Units CFU • In theory, one CFU arises from one cell - may not be true - may arise from clusters / chains of cells - may give an underestimation of the number of bacteria in a sample • Cells need to be separated - Sample homogenization - Sample dilution 18 • Countable plate contains 25- 250 colonies • Fewer or more colonies affect accuracy • Total number: multiply the colony count by the dilution factor • Expressed as bacteria per gram or ml of food 19 Analysis Roll Tube Method • Same as pour plate but tubes are used • Bacterial dilution is added to 2 ml molten agar in a tube and rolled around in cold water until solid • Advantage – less plate count agar is used 20